Perfectly Square at the top with just enough space to sew in the hook and eye.
Here's a view of the zipper sewn to the main fabric (Red) and the lining. Sew the lining at the neckline before you install the zipper. You can then under stitch your lining. You could do it all the way past the zipper, but I like to stop before the zipper so I have room to play without worrying that the under stitching may cause me problems. Take a close look at the picture above. See how I turn that zipper top out and away toward the seam allowance and sew it in place.
Here's where people make a critical error that may cause a bulky less than square finished top. They just fold that lining over (right sides together, sandwiching the zipper and sew from the neckline edge and down the zipper.
Here's the adjustment for a perfectly square finished zipper top. Turn the seam allowance to the inside (toward the lining).
Pin in place.
Now sew the lining to the fashion fabric.
Even tops with the space needed to insert the hook and eye.
